From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-21-ewr.dyndns.com (mxout-087-ewr.mailhop.org [216.146.33.87]) by lists.bufferbloat.net (Postfix) with ESMTP id 6BECF2E0044 for ; Sun, 20 Mar 2011 15:24:04 -0700 (PDT) Received: from scan-22-ewr.mailhop.org (scan-22-ewr.local [10.0.141.244]) by mail-21-ewr.dyndns.com (Postfix) with ESMTP id C27753315 for ; Sun, 20 Mar 2011 22:24:03 +0000 (UTC) X-Spam-Score: 0.0 () X-Mail-Handler: MailHop by DynDNS X-Originating-IP: 64.81.33.126 Received: from bifrost.lang.hm (mail.lang.hm [64.81.33.126]) by mail-21-ewr.dyndns.com (Postfix) with ESMTP id 974AC2BD0 for ; Sun, 20 Mar 2011 22:23:58 +0000 (UTC) Received: from asgard.lang.hm (asgard.lang.hm [10.0.0.100]) by bifrost.lang.hm (8.13.4/8.13.4/Debian-3) with ESMTP id p2KMIQtE002306; Sun, 20 Mar 2011 14:19:06 -0800 Date: Sun, 20 Mar 2011 15:18:26 -0700 (PDT) From: david@lang.hm X-X-Sender: dlang@asgard.lang.hm To: Jonathan Morton In-Reply-To: Message-ID: References: <4D7F4121.40307@freedesktop.org><20110315175942.GA10064@goldfish><1300212877.2087.2155.camel@tardy><20110315183111.GB2542@tuxdriver.com><29B06777-CC5F-4802-8727-B04F58CDA9E3@gmail.com><20110315205146.GF2542@tuxdriver.com><219C7840-ED79-49EA-929D-96C5A6200401@gmail.com><20110315151946.31e86b46@nehalam><1300228592.2087.2191.camel@tardy><1300229578.2565.29.camel@edumazet-laptop><87fwqo54n7.fsf@cruithne.co.teklibre.org><823E2A7B-4F46-4159-8029-BD3B075CC4CE@gmail.com><87bp1b6fo0.fsf@cruithne.co.teklibre.org><87bp1b4yh4.fsf@cruithne.co.teklibre.org> <7480559F-1F3B-4CE5-939F-FD9FD3E68E52@cisco.com> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: Stephen Hemminger , bloat Subject: Re: [Bloat] Random idea in reaction to all the discussion of TCPflavours - timestamps? X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 20 Mar 2011 22:24:04 -0000 On Sun, 20 Mar 2011, Jonathan Morton wrote: > I think we can come up with some simple empirical rules for choosing queue sizes. I may be half-remembering something VJ wrote, but here's a starting point: > > 0) Buffering more than 1 second of data is always unacceptable. what about satellite links? my understanding is that the four round trips to geosync orbit (request up, down, reply up down) result in approximatly 1 sec round trip. David Lang > 1) Measure (or estimate) the RTT of a full-sized packet over the exit link and back, then add 100ms for typical Internet latency, calling this total T1. If T1 is more than 500ms, clamp it to 500ms. Calculate T2 to be twice T1; this will be at most 1000ms. > > 2) Measure (or estimate) the throughput BW of the exit link, in bytes per second. > > 3) Calculate ideal queue length (in bytes) Q1 as T1 * BW, and the maximal queue length Q2 as T2 * BW. These may optionally be rounded to the nearest multiple of a whole packet size, if that is convenient for the hardware. > > 4) If the link quality is strongly time-varying, eg. mobile wireless, recalculate Q1 and Q2 as above regularly. > > 5) If the link speed depends on the type of equipment at the other end, the quality of cabling, or other similar factors, use the actual negotiated link speed when calculating BW. When these factors change, recalculate as above. > > I would take the "hysteresis limit" to be an empty queue for the above algorithm. > > - Jonathan > > _______________________________________________ > Bloat mailing list > Bloat@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/bloat >